The 12SQ7GT/G is a double diode triode with heaters designed to operate from the 12.6 volts available in a vehicle. The diodes are for AM signal detection and AGC detection whilst the triode section is for first audio amplification. This is typical for a valve used in a radio superhet receiver.
Apart from the 12.6 volt heaters the valve characteristics are equal to the 6SQ7 the GT is for glass tubular construction.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 60 mm tall.
References: Datasheet, 1040 & 1043. Type 12SQ7GT/G was first introduced in 1939.
Absolute Maximum Operating Conditions¶
Updated February 21, 2013. shape:wide.glass.tube construction:pinch type:double.diode.triode age:1930.1940 base:io heater:12.6v pins:8 pin:1.m pin:2.g1 pin:3.k pin:4.a(d2) pin:5.a(d1) pin:6.a pin:7.h pin:8.h